<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <div id="app">
    <div class="box">
      <h3>
        小黑售货机
      </h3>
      <button @click="buy(5)">
        可乐5元
      </button>
      <button @click="buy(10)">
        咖啡10元
      </button>
    </div>

    <p>
      银行卡余额：{{money}}元
    </p>
  </div>

  <script src="https://cdn.jsdelivr.net/npm/vue@2.7.16/dist/vue.js"></script>
  <script>
    const app = new Vue({
      el: '#app',
      data: {
        money: 100
      },
      methods: {
        buy(price) {
          if (this.money >= price) {
            this.money -= price
            alert('购买成功')
          } else {
            alert('余额不足')
          }
        }
      }
    })
  </script>
</body>

</html>